Here is my dash now after following your advice thanks Tony :
I've done a bit more testing and it seems that the fuel and oil pressure gauges have both failed.
I'm getting 12v across them as you would expect, so the wiring is good. I'm thinking the fuel gauge is the same as the oil pressure - i.e. full scale when the sender wire is disconnected ? The senders are both going to earth with the engine stopped and minimal fuel in the tank, so I think that's good ?
I think on balance I'm happier to be able to just fit new gauges, rather than be worrying about some kind of wiring loom and/or sender failures ?
I'm now stuck trying to remove the illumination connectors/bulbs - any thoughts ? Am I just not pulling/wiggling hard enough or is there a trick to getting them out ? (clearly I am worried about breaking something, so haven't been too brutal).
I'm definitely not looking forward to refitting the speedo cable by the way - getting it out was very tight, probably because it goes beyond the brake pipes in the engine bay, so I couldn't quite push the dash as far out as I wanted before having to disconnect.
Cheers,